A Moment of Science

The Straight-up Tower of Pisa?

By
A Moment of Science Staff

Posted September 27, 2003

The Leaning Tower of Pisa can’t lean too much more or it will fall over. Today, on A Moment of Science, we’ll learn how this dilemma is being dealt with.

According to my calculations, the leaning Tower of Pisa is leaning about an inch less than it was the last time I visited. How is that? Well, the Tower of Pisa leans south because it was built on a very soft soil that shifts because of the fluctuation of a water table below the surface. The problem was that if the tower started leaning too far in one direction, it would topple over.

After doing some modeling, scientists tried using a special drill to extract soil from underneath the north side of the tower. The drill was designed not to disturb the ground on the way in, but to extract between fifteen and twenty liters of soil on the way out. This left a cavity which closed gently, causing the tower to shift. After drilling at several different points, not only did the tower move northward, but the sunken south side actually came up a little.

As you know, the whole appeal of the tower of Pisa is that it leans. In order to achieve such a lean, the plan is to correct the tilt only a little bit, so that most people won’t notice the change. After all, even a relatively small shift will add years to the life of the tower. And all that extra time will enable scientists to explore other ways of keeping the tower from shifting, like isolating the ground immediately underneath the tower so that it won’t be affected by the water table.

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